Detectives raided Mr. Park’s photo studio in eastern Seoul in the fall. They later interrogated him several times for resending such North Korean propaganda postings as “Long Live Kim Jong-il!”

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In an interview in December, Mr. Park said his Twitter posts were meant to lampoon the North Korean regime. Mr. Park, a member of the Korean Socialist Party, said he supported its platform, which criticized the Pyongyang government’s human rights policy and its hereditary transfer of power.

“It was humiliating and ludicrous to have to wear a straight face and explain all my jokes to the detectives,” said Mr. Park, who faces up to seven years in jail if convicted.

Prosecutors charged that joke or no joke, Mr. Park’s Twitter account served as a tool to spread North Korean propaganda.

The article notes that prosecutions under this law have increased since the current administration took power.

In 2010, 151 people were interrogated on suspicion of violating the law, up from 39 in 2007. The number of people prosecuted on charges of pro-North Korean online activities increased to 82 in 2010 from five in 2008, according to government data submitted to lawmakers. During the first 10 months of 2011, the police deleted 67,300 Web posts they believed threatened national security by “praising North Korea and denouncing the U.S. and the government,” a sharp rise from 14,430 posts in 2009.

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South Korea still blocks its citizens’ access to North Korean Web sites, though North Korea has recently gone around the firewalls by using Twitter accounts. The South’s policy has left the delivery and interpretation of North Korean announcements in the hands of a relatively small group of officials and journalists with special access to North Korean media.